1. Field of the Invention
The present invention relates to a circuit module, and in particular to a circuit module mounting thereon a semiconductor circuit chip used for a high frequency bandwidth of a microwave, a milliwave, or the like.
2. Description of the Related Art
FIGS. 11A and 11B are cross-sectional diagrams of a prior art circuit module; FIG. 11A shows a partially cross-sectional diagram along a line A-A shown in FIG. 11B. FIG. 11B shows a cross-sectional diagram along a line B-B shown in FIG. 11A. In FIGS. 11A and 11B, a ground metal layer 2 is formed above a chip mounting dielectric substrate 1. Above the chip mounting dielectric substrate 1, a signal line 5a is also formed together with the ground metal layer 2. The signal line 5a is connected to a signal line 5 through a metal bump 3. A ground metal layer 4 is formed on a surface of a semiconductor circuit chip 6 on which devices are mainly mounted, in the form of flip-chip.
Also, a cap 9 is formed so as to cover both of the dielectric substrate 1 and the semiconductor circuit chip 6, thereby preventing its breakage and sealing off the semiconductor circuit chip 6. It is to be noted that the signal line 5a is connected to the signal line 5b through a through-hole 8 passing through the dielectric substrate 1, and is further connected to an external circuit.
Besides the above-mentioned circuit module, for a circuit module for a high frequency bandwidth, a high frequency package module has been proposed in which the semiconductor circuit chip is mounted on the dielectric substrate in the form of flip-chip. In this high frequency package module, a plurality of land patterns whose sizes are equal to or less than ½ of a wavelength λ of an operation frequency of the semiconductor circuit chip are formed on a side opposite to the side on which the semiconductor circuit chip of the dielectric substrate is mounted and opposed to the semiconductor circuit chip. Also, a plurality of through-holes filled with metal are formed at intervals of equal to or less than λ/4 in a mounting area above the semiconductor circuit chip of the dielectric substrate (see patent document 1).
In addition, there has been proposed a high-frequency module which can considerably reduce radiation of electromagnetic waves from a surface of a circuit substrate and can suppress a characteristic fluctuation by an attachment of a cap in an arrangement where ground patterns are formed on the highest layer and the lowest layer over the circuit substrate of the module and a circuit pattern which becomes a high-frequency transmission line is formed on an internal layer of the circuit substrate (see e.g. patent document 2).
[Patent Document 1] Japanese Patent Application Laid-open No. 2003-78066
[Patent Document 2] Japanese Patent Application Laid-open No. 2005-209921
In the circuit module as shown in FIGS. 11A and 11B, there has been a problem that unnecessary radiation waves leaking from e.g. the back side (side opposite to the chip mounting dielectric substrate 1, where no circuit is mounted) of the semiconductor circuit chip return to the semiconductor circuit chip 6 through the signal line 5a→metal bump 3→signal line 5, thereby deteriorating the isolation and disturbing a normal operation of the semiconductor circuit chip 6.
For this reason, by affixing a rubber-based wave absorber or the like inside of the cap 9, leaking power has been absorbed. However, the rubber-based wave absorber has been weak in secular variation or aging phenomena, so that there has been a problem in a long-term reliability. Also, there has been fear that if not the rubber-based wave absorber but an organic wave absorber is used, occurrence of out-gas affects the reliability on the semiconductor circuit chip.